OK so I ignored the oil and left the timing alone - but the miss is still there and maybe getting worse. I have tried a different O-Ring, changed the needle settings and cleaned the jets countless times.
The problem was annoying before but only came on under at higher revs but I have now replaced the 13 tooth front sprocket with a 9 tooth and everything is now at higher revs.
It is supposed to use a resistor plug and it has one but is it possible the resistor can fail causing issues with the CDI ? ( I have ordered new plugs) I did fit a non R plug and the problem was no better or worse.
Or should I be looking for a faulty earth